The present invention is directed to a hand held machine tool with a safety device, in particular for protecting the tool operator when water penetrates into the tool handle or when the tool housing develops a conducting connection with the power supply because of water or conductive dirt or in some other comparable manner.
In German patent 950 658, a protective device for a hand held machine tool is disclosed, driven by an electric motor, which is separated from the metal parts of the tool housing by insulated parts and with bare electrodes located within the tool housing at locations most exposed to dust or dirt. The electrodes are connected to ground or with a neutral point in the power supply network and serve to dissipate leakage currents. This safety device does not function when the neutral or ground conductor, connected with the electrode, is interrupted. When water penetrates into the housing, there is the danger that, because of the longer "water leakage paths", a not inconsiderable portion of the leakage currents, possibly present, are dissipated over the operator to ground. Additionally, such an arrangement leads to slight electric shock, in severe cases, however, it may lead to an electrical accident.
The German Auslegeschrift 1 105 977 discloses a leakage current protection for which a short-circuit current, passing over a dirty insulating material carrier to bare electrodes, can cause an overcurrent protection circuit breaker, usually disposed in the power supply network, to respond. This leakage current protection functions independently of the grounded conductor. This device, intended to protect against leakage current and located in the interior of the protective housing, which is preferably exposed to contamination during the operation of the hand-held machine tool, cannot effectively protect the user, especially in the case of water entering the tool housing, but also in the case of other types of contamination, since modern overcurrent protection circuit breakers, usually disposed in power supply networks, normally respond only to currents 16 A or greater.